Projector with fan controller

This application is based on application No. 2000-209998 filed in Japan.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projector for projecting images.

2. Description of the Background Art

A projector utilizing liquid crystal panels controls these panels based on image signals, and guides light from a lamp to the panels and then to the screen, thereby projecting images on the screen. The lamp used in such a projector has high intensity because images formed on the liquid crystal panels are projected as magnified images by using an optical system. Being irradiated in a high illumination, the liquid crystal panels get hot. The liquid crystal panels realize image display by partly shielding the light from the lamp using a polarizer, so that the vicinity of the polarizer gets hot in particular.

It has been conventionally conducted to cool the liquid crystal panels by supplying the panels with a current of air from a cooling fan.

However, the fan makes untoward noises. Since the recent projectors use a fan having a high blowing capability in keeping with the high intensity of the lamp, the fan makes more noises.

In the case of a rear-projection type television system with a projector, the cooling fan is stored in a large casing and used in an ordinary household, so that the noise reduction of the fan is an important issue.

SUMMARY OF THE INVENTION

According to the present invention, a projector comprising: a light source; an optical system for guiding light from the light source to an projective region; a display device for modulating the light from the light source, based on image signals, the display device being arranged in a light path of the optical system; at least one fan for cooling the display device; and a fan controller for receiving signals based on the image signals and varying a number of revolutions of the at least one fan in accordance with changes in the image signals.

Thus, in the projector, the number of revolutions of at least one fan is varied in accordance with changes in the image signals, which makes it possible to reduce unnecessary noise caused by the fan.

In an aspect of the present invention, the fan controller receives signals based on voice signals, and changes the number of revolutions of the at least one fan in accordance with changes in the voice signals.

Thus, in the projector, the number of revolutions of at least one fan is varied in accordance with changes in the voice signals, which makes it possible to reduce untoward noises caused by the fan.

In another aspect of the present invention, while changing the number of revolutions of the at least one fan, the fan controller provides fluctuations to the numbers of revolutions.

Thus, the number of revolutions of at least one fan is given fluctuations, which makes it possible to reduce untoward noises caused by the fan.

In another aspect of the present invention, the projector further comprises a memory for storing data concerning cumulative amount of lighting time of the light source, wherein the fan controller reduces the number of revolutions of the at least one fan, as the cumulative amount of lighting time becomes larger.

Thus, the noises caused by the fan can be reduced in accordance with a decrease in intensity of the light source.

In another aspect of the present invention, the display device has a plurality of component devices corresponding to a plurality of colored lights; the at least one fan includes a plurality of fans arranged separately in correspondence with the plurality of component devices so as to cool the plurality of component devices separately; and the fan controller controls the number of revolutions of the plurality of fans separately, based on the image signals corresponding to the plurality of colored lights.

Thus, in the projector, a plurality of fans can be individually controlled.

In further another aspect of the present invention, the display device is a single device for displaying images based on color image information; the at least one fan is a single fan for cooling the single device; and the fan controller changes the number of revolutions of the single fan in accordance with changes of G and B color components contained in the image signals.

Thus, in the projector, the control of the fan can be simplified.

According to the present invention, a projector comprising: a screen; a main-body casing which forms the outside shape of the projector and in which the screen is installed; a light source; an optical system for guiding light from the light source to the screen; a display device for modulating the light from the light source, based on image signals, the display device being arranged in a light path of the optical system; at least one fan for cooling the display device; and a fan controller for receiving signals based on the image signals and varying a number of revolutions of the at least one fan in accordance with changes in the image signals.

Therefore, noises can be reduced in the case with a screen and a main-body casing additionally provided.

Thus, the object of the present invention is to realize a reduction in noise (including substantial noise reduction of eliminating grating noise) caused by the cooling fan in a projector.

These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of the projector of a first preferred embodiment;

FIG. 2 shows the structure involving the control of the fan and other structures;

FIG. 3 shows the inner structure of the television system of a second preferred embodiment;

FIG. 4 shows the structure of the projector; and

FIG. 5 shows the structure involving the control of the fan with other structures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

<1. First Preferred Embodiment>

FIG. 1 shows the structure of the projector <b>1</b> of the first preferred embodiment of the present invention. FIG. 1 is illustrated in a simplified manner to make the internal components understood better.

The projector <b>1</b> comprises, inside its cover <b>10</b>, a light source unit <b>20</b> for generating light for projection; an optical system <b>30</b> for dividing the light from the light source unit <b>20</b> into color light of red (R), green (G), and blue (B); three liquid crystal panels <b>41</b>, <b>42</b>, and <b>43</b> for individually providing the red, green, and blue light with image data (non-uniform light intensity corresponding to images) by partly shielding each of the color light; a synthesizing prism <b>51</b> for synthesizing color light that has passed the liquid crystal panels; and a lens unit <b>50</b> for projecting the synthesized light at the screen installed in a predetermined projecting position.

To be more specific, the optical system <b>30</b>, the synthesizing prism <b>51</b> and the lens unit <b>50</b> compose a projective optical system which guides the light from the light source unit <b>20</b> to the screen, and the three liquid crystal panels <b>41</b>-<b>43</b> are arranged on a light path of the projective optical system.

On the cover <b>10</b> are provided three fans <b>611</b>, <b>612</b>, and <b>613</b> for cooling the liquid crystal panels <b>41</b>, <b>42</b>, and <b>43</b>; the currents of air from these fans <b>611</b>-<b>613</b> are guided to the liquid crystal panels <b>41</b>-<b>43</b> through respective ducts <b>62</b>. In FIG. 1, the currents of air caused by the fans <b>611</b>-<b>613</b> flow from the back side towards the front side of paper, or in the direction along the surfaces of the liquid crystal panels <b>41</b>-<b>43</b>, and then are discharged.

In the following description, the liquid crystal panels <b>41</b>-<b>43</b> are distinguished from each other by being respectively referred to as the G liquid crystal panel <b>41</b>, the R liquid crystal panel <b>42</b>, and the B liquid crystal panel <b>43</b> corresponding to the red, the green, and the blue light, respectively. The fans <b>611</b>-<b>613</b> leading to the liquid crystal panels <b>41</b>-<b>43</b> are respectively referred to as the fan <b>611</b> for G panel, the fan <b>612</b> for R panel, and the fan <b>613</b> for B panel.

The light source unit <b>20</b> has a discharge lamp <b>21</b> as a light source, and the light from the lamp <b>21</b> is discharged towards the optical system <b>30</b>. Since the lamp <b>21</b> gets hot, the cover <b>10</b> is further provided with a fan <b>63</b> for cooling the lamp <b>21</b>.

The light from the light source unit <b>20</b> is converted into polarized light whose intensity distribution is approximately uniform by a lens array <b>311</b>, a PBS prism (polarized-beam separating prism) <b>312</b>, a lens array <b>313</b>, and a cemented lens <b>314</b> of the optical system <b>30</b>.

The light which has passed the cemented lens <b>314</b> is divided by a dichroic mirror <b>321</b> into red light and light of the other components; the red light is guided to the R liquid crystal panel <b>42</b> via a mirror <b>322</b> and a lens <b>331</b>.

The light of the other components from the dichroic mirror <b>321</b> is further divided by another dichroic mirror <b>323</b> into green light and blue light. The green light is guided to the G liquid crystal panel <b>41</b> via a lens <b>332</b>, while the blue light is guided to the B liquid crystal panel <b>43</b> via a lens <b>333</b>, a mirror <b>324</b>, a lens <b>334</b>, a mirror <b>325</b>, and a lens <b>335</b>.

The three liquid crystal panels <b>41</b>-<b>43</b> supply the color light of red, green, and blue with data about the red, green, and blue components of images to be projected. Later, the synthesizing prism <b>51</b> synthesizes image light which reflects one color image.

The light synthesized by the synthesizing prism <b>51</b> is guided to the screen which forms a projective region by the lens unit <b>50</b> having a plurality of lenses for projection, so that a color image can be projected on the screen.

FIG. 2 is a block diagram showing the structure involving the control of the fans <b>611</b>-<b>613</b> together with the other structures. The projector <b>1</b> comprises, as the structure involving the control of the fans <b>611</b>-<b>613</b>, an image signal process unit <b>71</b> for generating image signals to be given to the three liquid crystal panels <b>41</b>-<b>43</b>, based on the image signals sent from a signal generation device <b>81</b>; a voice signal process unit <b>72</b> for generating voice signals to be given to a speaker <b>82</b>, based on the voice signals sent from the signal generation device <b>81</b>; a fan control unit <b>73</b> for generating control signals of the fans <b>611</b>-<b>613</b>; a fluctuation signal generation unit <b>74</b> for generating signals to provide the numbers of revolutions of the fans <b>611</b>-<b>613</b> with fluctuations; a lighting circuit <b>75</b> for lighting up the lamp <b>21</b>; and a lighting time recording unit <b>76</b> for recording the cumulative amount of lighting time.

As the signal generation device <b>81</b>, any device such as a tuner, a computer, or a VTR can be used. The signal generation device <b>81</b> and the speaker <b>82</b> can be either united or not united with the projector <b>1</b>.

The structure involving the control of the fans <b>611</b>-<b>613</b> can be constructed as a special electric circuit, or can be realized by making the CPU perform some of the calculation process in accordance with a program.

The image signal process unit <b>71</b> generates the R component, the G component, and the B component of image signals (hereinafter referred to as the R image signal, the G image signal, and the B image signal) sent from the signal generation device <b>81</b>. These R, G, and B image signals are given to the R liquid crystal panel <b>42</b>, the G liquid crystal panel <b>41</b>, and the B liquid crystal panel <b>43</b>, respectively.

The image signal process unit <b>71</b> comprises a level calculation unit <b>711</b> for finding the levels of the R, G, and B image signals (which correspond to the mean value of the intensities of all the color components of the entire image region, and which are hereinafter referred to as intensity levels), and the intensity levels of the R, G, and B are entered into the fan control unit <b>73</b>.

In the same manner, the voice signal process unit <b>72</b> comprises a level calculation unit <b>721</b> for finding the levels of voice signals (hereinafter referred to as voice levels), and the voice levels found are entered into the fan control unit <b>73</b>.

The fluctuation signal generation unit <b>74</b> generates fluctuation signals for providing the numbers of revolutions of the fans <b>611</b>-<b>613</b> with time fluctuation, and the fluctuation signals generated are entered to the fan control unit <b>73</b>.

The lighting time recording unit <b>76</b> records the cumulative amount of lighting time of the lamp <b>21</b> to a nonvolatile memory <b>761</b> upon receipt of the signal from the lighting circuit <b>75</b>. The contents recorded in the memory <b>761</b> are entered to the fan control unit <b>73</b>. When the lamp <b>21</b> is replaced, the cumulative amount of lighting time stored in the memory <b>761</b> is reset.

The following is a description of how the fans <b>611</b>-<b>613</b> are controlled by the fan control unit <b>73</b> which receive signals from the level calculation unit <b>711</b>, the level calculation unit <b>712</b>, the fluctuation signal generation unit <b>74</b> and the lighting time recording unit <b>76</b>.

In a projector which performs image projection by supplying the light from the light source with image data, or with non-uniform intensities corresponding to images by using a display device, when a white image is projected, most part of the light from the light source is guided to the projective region by the display device. On the other hand, when a black image is projected, most of the light from the light source is absorbed (or can be reflected or scattered) by the display device so as to be shielded. Consequently, when a black image is projected, the display device (in the vicinity of the display device in the case where light is reflected to be shield) gets hot.

In a projector using liquid crystal panels as a display device, the light from the light source is supplied with image data by the polarizers of the liquid crystal panels absorbing the light. As a result, when a dark image is projected, the liquid crystal panels (polarizers in particular) get hot. In the prior art projector using liquid crystal panels, when a black image is projected, the cooling fan is continuously revolved at a sufficiently high number of revolutions so as not to cause the liquid crystal panels to be damaged by heat. Consequently, high noises occur continuously. To avoid this problem, the projector <b>1</b> performs noise reduction control by reducing the numbers of revolutions of the fans <b>611</b>-<b>613</b> when the liquid crystal panels <b>41</b>-<b>43</b> absorb a little light.

In the three-panel type projector <b>1</b> which uses three liquid crystal panels <b>41</b>-<b>43</b> as component devices and which composes a display device from three liquid crystal panels <b>41</b>-<b>43</b>, the R liquid crystal panel <b>42</b> has less heat when the image has a bright R component; the G liquid crystal panel <b>41</b> has less heat when the image has a bright G component; and the B liquid crystal panel <b>43</b> has less heat when the image has a bright B component. Therefore, the level calculation unit <b>711</b> of the image signal process unit <b>71</b> finds the intensity levels of the R, G, and B image signals or the illumination of the R, G, and B components of the image to be projected. Then, the intensity levels found are entered to the fan control unit <b>73</b> so as to control the numbers of revolutions of the fans <b>611</b>-<b>613</b>.

The fan control unit <b>73</b> includes control circuits <b>731</b> which individually control the numbers of revolutions of the fans <b>611</b>-<b>613</b>. The intensity levels of the R, G, and B image signals are entered to the control circuits <b>731</b> respectively connected to the fan <b>612</b> for R panel, the fan <b>611</b> for G panel, and the fan <b>613</b> for B panel. The numbers of revolutions of the fans <b>611</b>-<b>613</b> are individually controlled so that they can be decreased with increasing intensity levels of these color components.

Thus, the number of revolutions of the fan <b>612</b> for R panel reduces when the R liquid crystal panel <b>42</b> has a little heat, the number of revolutions of the fan <b>611</b> for G panel reduces when the G liquid crystal panel <b>41</b> has a little heat, and the number of revolutions of the fan <b>613</b> for B panel reduces when the B liquid crystal panel <b>43</b> has a little heat. Consequently, unnecessary noises which would be caused by the fans <b>611</b>-<b>613</b> are suppressed, while the liquid crystal panels <b>41</b>-<b>43</b> are sufficiently cooled.

On the other hand, whether the noises caused by the fans are untoward or not depends on the circumstance where images are viewed; when there is a larger noise in the circumstance, the noise caused by the fans is not important. Therefore, in the projector <b>1</b>, the level calculation unit <b>721</b> of the voice signal process unit <b>72</b> finds the voice levels and enters them to the fan control unit <b>73</b>, and increases the numbers of revolutions of the fans <b>611</b>-<b>613</b> with increasing voice level, so as to achieve sufficient cooling.

Each control circuit <b>731</b> performs reducing the number of revolutions with increasing intensity level and increasing the number of revolutions with increasing intensity level, which could be synthesized in various manners. For example, it is possible that while the control based on the intensity levels is being performed, the number of revolutions can be gradually increased in accordance with an increase in voice level. If the number of revolutions, which is as a rule controlled in accordance with the voice levels, goes below the number of revolutions found from the intensity levels, the number of revolutions can be controlled to be in accordance with the intensity levels.

The cumulative amount of lighting time entered from the lighting time recording unit <b>76</b> to the fan control unit <b>73</b> is used to control the change of the numbers of revolutions of the fans <b>611</b>-<b>613</b> found based on the intensity levels and the voice levels. Since the lamp <b>21</b> loses its intensity as its cumulative time of lighting becomes longer, the liquid crystal panels <b>41</b>-<b>43</b> have less heat as the cumulative time of lighting becomes longer. Therefore, it would unnecessarily increase noises if the fans <b>611</b>-<b>613</b> were operated at the numbers of revolutions determined in accordance with the performance of a brand-new lamp <b>21</b>, when the lamp <b>21</b> has been used for a long time period.

The fan control unit <b>73</b> refers to the cumulative amount of lighting time stored in the memory <b>761</b> and decreases the numbers of revolutions of the fans <b>611</b>-<b>613</b> as the cumulative amount of lighting time becomes larger. As a result, the unnecessarily increase in noise is prevented.

In the projector <b>1</b>, the fan control unit <b>73</b> further receives fluctuation signals from the fluctuation signal generation unit <b>74</b>. The fluctuation signals give fluctuations to the numbers of revolutions of the fans <b>611</b>-<b>613</b> determined based on the voice levels and the cumulative amount of lighting time, or correspond to noise signals given to the signals which control the revolutions.

Fluctuations generally indicate nonperiodic changes; the fluctuations given to the numbers of revolutions by the fluctuation signal generation unit <b>74</b> can include semi-nonperiodic changes having a long cycle. By using, as fluctuations, so-called 1/f noises whose amplification (or the amount of change in the number of revolutions) is decreased with increasing frequencies, discomfort (a feeling of grating) caused by the fans <b>611</b>-<b>613</b> can be further reduced.

The fluctuation signals can be given to the fan <b>63</b> for a lamp. As a result, the grating noise caused by the fan <b>63</b> for a lamp can be reduced.

As described hereinbefore, the projector <b>1</b> finds the intensity levels of the R, G, and B components of images, and individually decreases the numbers of revolutions of the fans as each of the intensity levels gets higher. This makes it possible to keep tabs on the numbers of revolutions in accordance with the image signals, preventing the occurrence of unnecessarily high noises. When the voice levels are high, the numbers of revolutions of the fans <b>611</b>-<b>613</b> can be increased to increase the cooling effects.

Further, the occurrence of unnecessary noises can be reduced in accordance with the cumulative amount of lighting time of the lamp <b>21</b>, and the provision of the fluctuations to the numbers of revolutions of the fans <b>611</b>-<b>613</b> can reduce the grating noises.

The reduction in the numbers of revolutions of the fans <b>611</b>-<b>613</b> realizes a reduction in power consumption.

&lt;2. Second Preferred Embodiment&gt;

FIG. 3 shows the internal structure of the rear-projection type television system <b>100</b> of the second preferred embodiment of the present invention.

The television system <b>100</b> has a screen <b>102</b> which forms a projective region and on which images are projected from behind, at the front side of a casing <b>101</b> forming an outer main body. The casing <b>101</b> includes a projecting unit <b>1</b><i>a </i>and a mirror <b>103</b> for guiding the light from the projecting unit <b>1</b><i>a </i>to the screen <b>102</b>. The casing <b>101</b> further includes a tuner <b>81</b><i>a </i>for transmitting image signals and voice signals to the projecting unit <b>1</b><i>a </i>and a speaker <b>82</b> for giving off voices, based on the voice signals from the projecting unit <b>1</b><i>a. </i>

FIG. 4 shows the structure of the projecting unit <b>1</b><i>a. </i>FIG. 4 is illustrated in a simplified manner so that the internal structure can be understood better. The same components as those in the first preferred embodiment are referred to with the same symbols.

The projecting unit <b>1</b><i>a </i>is a so-called single-plate type projector comprising, inside the cover <b>10</b>, a light source unit <b>20</b> for generating light for projection, a single liquid crystal panel <b>4</b>, an optical system <b>30</b> for guiding the light from the light source unit <b>20</b> to the liquid crystal panel <b>4</b>, and a lens unit <b>50</b> for emitting the light passed through the liquid crystal panel <b>4</b>.

The cover <b>10</b> is provided with a fan <b>61</b> for cooling the liquid crystal panel <b>4</b>, and the current of air from the fan <b>61</b> is guided to the liquid crystal panel <b>4</b> via a duct <b>62</b>. In FIG. 4, the current of air from the fan <b>61</b> flows in the direction from the back side to the front side of the paper, or along the surface of the liquid crystal panel <b>4</b>, and then is discharged.

Similar to the first preferred embodiment, the light source unit <b>20</b> has a discharge lamp <b>21</b> as a light source, and the cover <b>10</b> is further provided with a fan <b>63</b> for cooling the lamp inside the light source unit <b>20</b>.

The light from the light source unit <b>20</b> is converted into polarized light having an approximately uniform intensity dispersion by a polarizing conversion element <b>341</b>, lens arrays <b>342</b>, <b>343</b>, and a cemented lens <b>344</b>.

The light passed through the cemented lens <b>344</b> is divided into color light of R, G, and B proceeding in slightly different directions by three dichroic mirrors <b>353</b> via mirrors <b>351</b> and <b>352</b>, and goes into a field lens <b>354</b>. As a result, the light having R, G, and B components is gathered and goes into pixels corresponding to the R, G, and B of the liquid crystal panel <b>4</b>, and the light passing through the liquid crystal panel <b>4</b> is given color image data.

The light passed through the liquid crystal panel <b>4</b> is emitted from the lens unit <b>50</b>, reflected by the mirror <b>103</b>, and guided to the screen <b>102</b> so as to project color image onto the screen <b>102</b> as shown in FIG. <b>3</b>.

FIG. 5 is a block diagram showing the structure involving the control of the fan <b>61</b> for liquid crystal panel in the projecting unit <b>1</b><i>a. </i>Similar to the projector <b>1</b> of the first preferred embodiment, the projecting unit <b>1</b><i>a </i>comprises an image signal process unit <b>71</b>, a voice signal process unit <b>72</b>, a fan control unit <b>73</b>, a fluctuation signal generation unit <b>74</b>, a lighting circuit <b>75</b>, and a lighting time recording unit <b>76</b>.

These components have the same functions as those in the first preferred embodiment except that the image signal process unit <b>71</b> generates image signals given to the liquid crystal panel <b>4</b> based on the image signals sent from the tuner <b>81</b><i>a, </i>and the fan control unit <b>73</b> controls the fan <b>61</b> for liquid crystal panel.

The structure involving the control of the fan <b>61</b> can be constructed as a special electric circuit, or can be realized by making the CPU perform some of the calculation process in accordance with a program.

The GB signal level calculation unit <b>711</b><i>a </i>of the image signal process unit <b>71</b> finds the intensity levels of the G image signals and the B image signals combined (that is, the intensity levels of cyan). The intensity levels of G and B are entered to the fan control unit <b>73</b>. When these intensity levels are high, the fan control unit <b>73</b> reduces the number of revolutions of the fan <b>61</b>.

In the GB signal level calculation unit <b>711</b><i>a, </i>the intensity levels of the G and B image signals combined are found because the energy level of the light of the R component is small enough not to greatly affect an increase in temperature of the liquid crystal panel <b>4</b>. On the other hand, the light of the G component and the light of the B component have approximately the same energy level. Therefore, proper cooling can be realized only by using the intensity levels of the G and B image signals combined. Using the G and B image signals can reduce the amount of calculation process to find the intensity levels, as compared with the case where all of the R, G, and B image signals are used, thereby simplifying the control.

Similar to the first preferred embodiment, in the projecting unit <b>1</b><i>a, </i>voice levels are found in the level calculation unit <b>721</b> of the voice signal process unit <b>72</b> and entered to the fan control unit <b>73</b>. The number of revolutions of the fan <b>61</b> is increased as the voice levels get higher so as to perform sufficient cooling.

The cumulative amount of light time of the lamp <b>21</b> is recorded by the lighting time recording unit <b>76</b> connected to the lighting circuit <b>75</b> and then entered into the fan control unit <b>73</b>. Thus, the number of revolutions of the fan <b>61</b> is reduced as the cumulative amount of lighting time of the lamp <b>21</b> becomes larger. The fan control unit <b>73</b> further receives signals from the fluctuation signal generation unit <b>74</b> so as to give fluctuations to the number or revolutions of the fan <b>61</b>.

As described hereinbefore, the projecting unit <b>1</b><i>a </i>of the television system <b>100</b> finds the intensity levels of the G and B components of images combined, and decreases the number of revolutions of the fan <b>61</b> as the intensity levels get higher. This makes it possible to control the number of revolutions in accordance with the image signals, preventing the occurrence of unnecessarily high noises. When the voice levels are high, the number of revolutions of the fan <b>61</b> can be increased to increase the cooling effects.

Further, the occurrence of unnecessary noises can be reduced in accordance with the cumulative amount of lighting time of the lamp <b>21</b>, and the provision of the fluctuations to the number of revolutions of the fan <b>61</b> can reduce the grating noises.

In particular, according to the television system <b>100</b>, the projecting unit <b>1</b><i>a </i>is stored in the casing <b>101</b> and used in an ordinary household under severe noise control guidelines, so that the reduction in noise of the fan <b>61</b> or in discomfort caused by the noise becomes further effective.

&lt;3. Modified Examples&gt;

The preferred embodiments of the present invention have been described so far; the present invention is not restricted to them, and various modifications are possible.

In the above preferred embodiments, the transmission type liquid crystal panel is used as a device for display. Alternatively, as a display device for providing the projected light with image data, a reflective type liquid crystal panel or a DMD (digital micromirror device) can be used. In the case of the DMD which causes non-uniform intensities by reflecting light, the reflected light heats the vicinity of the DMD, so that the cooling by the wind is focused on the vicinity of the display device.

Thus, any device which can provide the light from the light source with image data can be used as the display device, and the cooling of the display device is not restricted to the display device itself, but can include heat-generating units caused by the display device.

The above description simply says that image are projected; images to be projected can be motion pictures or still pictures.

The level calculation unit <b>711</b> of the image signal process unit <b>71</b> in the first preferred embodiment can be provided as three special electric circuits for calculating the intensity levels corresponding to the color components.

In the projector <b>1</b> or the projecting unit <b>1</b><i>a, </i>voice signals are outputted to the speaker <b>82</b>; however, instead, voice signals can be entered directly to the speaker <b>82</b> via the signal generation device <b>81</b> or the tuner <b>81</b><i>a. </i>

Although in the above preferred embodiments the revolutions of the fans are control by using the intensity levels or voice levels, the intensity levels of voice levels can be calculated as an average level in a predetermined short time, or can be found as a maximum value in a predetermined short time. Thus, it is not necessary to find the intensity levels or the voice levels strictly; any value can be used as long as it is an indicator of changes in time of the approximate illumination of the images or of the size of the voices.

In receiving a television broadcast, the number of revolutions of the fan for liquid crystal panel can be increased while commercials are being on the air, so as to increase the cooling efficiency temporarily.

The three-plate type projector <b>1</b> in the present preferred embodiment can be used as the rear-projection type television system of the second preferred embodiment, whereas the single-plate type projecting unit <b>1</b><i>a </i>in the second preferred embodiment can be used as the projector separate from a screen as in the first preferred embodiment.

In the second preferred embodiment, the GB signal level calculation unit <b>711</b><i>a </i>finds the intensity levels; however, when there is no need of reducing the calculation process, the intensity levels can be found from the R, G, and B image signals.

Furthermore, it is not necessary that the number of fans for liquid crystal panel and the number of the liquid crystal panels should be equal. For example, a plurality of fans can be provided for a single liquid crystal panel, while a plurality of liquid crystal panels can be cooled by a single fan.

While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous other modifications and variations can be devised without departing from the scope of the invention.